Currently, various methods are being used to combat this concern. Some of which include: metal detectors, vapour detectors, X-ray machines, and dogs. Many countries are putting forth great effort in developing new methods for inspection of the human body based on new physical principles: Nuclear Quadrupole Resonance (NQR), Raman backscattering, dielectric portals, passive and active terahertz range devices, passive millimeter range radars and active microwave portals.
The aforementioned methods do not guarantee the required effectiveness of remote and covert inspection, thus, these devices are not capable to detect a “suicide bomber” in adequate time so that the necessary precautions can be taken before detonation of the explosive device. Another notable disadvantage of the currently used methods is non-automatic determination of the threat level of the detected object in addition to the high false alarms' rate. These obstacles make it nearly impossible to use these devices for inspection of a large number of people moving in transit.
Hence, the task of detecting explosive devices being carried by “suicide bombers” should allow for the following provisions:                Remote inspection;        Automatic inspection;        Detection of various types of objects (dielectric/metal objects);        Detection in real time;        Automatic system determining threat level of the detected object;        Covert inspection;        Independence of external conditions;        Safety for human health;        Possibility to bind data and threat signal for a specific individual;        Mobility and relatively low cost        
There is a current method of detection used for metallic and non-metallic explosive devices being concealed on a person. In this method, the receiving antenna focuses on a small area of the human body using electromagnetic waves coming from that region. A radiometer data is then processed in a processing module, and the intensity and the position of the beam is recorded. The measured intensity of the received signal is then displayed as luminous intensity. By analyzing the distribution of the luminous intensity, the presence or absence of metallic or non-metallic objects can be determined, see, for example, Russian Patent No. RU2133971.
The main disadvantage of this method is the low contrast of the received image. This method cannot clearly distinguish non-metallic objects from the human body while the dielectric for the used wave range is transparent.
A second method of target remote inspection in monitored space is to irradiate the inspected area with microwaves using two or more elemental emitters. In this method, a register signal is reflected from the monitored area using one or more parallel recording channels. Coherent processing of the reflected signal occurs and the data received is displayed, see, for example, U.S. Pat. No. 5,557,283.
Emitters and receivers of an electromagnetic field are placed in multiple predetermined positions. The final determination is made after analyzing a three-dimensional image received after digital processing of the radiation is recorded in broadband.
This method uses microwaves for irradiation of a monitored area in frequency bandwidth without correlating its width with radial space resolution of the monitored area image and recording the time interval during which coherent processing of the received reflected signal is possible. This brings on the following disadvantages:                The method cannot be used to inspect a moving object/target. When an object is moving in space during the recording of the reflected signal, the position of the object against the emitting/receiving antennas changes thus making it impossible to use coherent processing of the recorded signal. Non-coherent processing results in low resolution imaging if the direction of movement of the inspected object is unknown. Thus, covert inspection is not possible.        Low resolution imaging cannot be analyzed to obtain quantitative data about the dielectric permeability of objects (parts of the target) and their equivalent mass.        
Another method for remote inspection of a target in monitored space includes irradiation of the monitored area with microwaves using two or more elemental microwave emitters and recording the reflected signal from the monitored area using one or more parallel recording channels. Coherent processing of the recorded signal to receive maximal intensity values of restored configuration of scattering objects in the monitored area is dependent upon the distance from the elemental emitters to the target. A display of the information is obtained after processing by reconstructing a microwave image as several three-dimensional surfaces, see Russian Patent No. RU 2294549. The aforementioned technical solution was used as a prototype for the proposed invention.
The main disadvantages of the technical solution which was used as a prototype for the proposed invention are:                Low intensity of the signal reflected from an “air-dielectric” border—about 7% of intensity for dielectrics with dielectric permeability ˜3 (which is typical for explosives). Thus, the signal reflected from the “dielectric-body” border (˜90% of intensity) could drastically distort the three-dimensional surface representing the “air-dielectric” border which leads to errors when determining the presence of explosive material;        Only a small range of microwave radiation incidence and receiving angles in which radiation reflected from the “air-dielectric” border can actually be recorded. Usually this is due to the fact that the dielectric's surface tends to be rather smooth, when compared to the wave length of microwave range and scattering on the border takes the form of mirror reflection. Therefore, this method of inspection is useful only in a very small range of possible angles of inspection.        